Orally available compounds having an α4 integrin inhibitory effect that are useful as a therapeutic medicine or a preventive medicine for inflammatory disease in which an α4 integrin-dependent adhesion process is involved in pathological conditions have already been known. For example, Patent Literature 1 discloses a phenylalanine derivative represented by the general formula (1) or a pharmaceutically acceptable salt thereof, and a typical compound thereof has the following chemical structure.

Further, Patent Literature 1 shows the results of VCAM inhibitory activity (VCAM-1/α4β1 binding assay) and (VCAM-1/α4β7 binding assay).
Further, Patent Literature 2 also discloses a phenylalanine derivative represented by the general formula (1) below and having R12 (R13) N—X1-group at an end or a pharmaceutically acceptable salt thereof.

It is shown that this compound has high VCAM-1/α4β1 integrin inhibitory activity in the presence of serum as compared with the compound of Example 1 of Patent Literature 1. Further, Patent Literatures 3 and 4 also disclose compounds having an α4 integrin inhibitory effect.